From August 1, fuel excise will rise twice a year in line with inflation, after being locked at 38.1 cents since the Howard coalition government froze automatic indexation in 2001.

In its first year, the measure means motorists will pay about 60 cents more for a tank of petrol.

Facing questions from coalition MPs, Treasurer Joe Hockey agreed to model the tax hike's impact on people in rural and regional areas.

Another MP told the party meeting the government needed to do more to convince voters of its benefits.

Taking on the issue in parliament, Prime Minister Tony Abbott said every cent raised by the tax would go to roads.

"This is a budget which delivers in spades for country Australia," he said.

Labor seized on a comment by Finance Minister Mathias Cormann who told parliament reducing the "spending growth trajectory" would impact on individuals, families, pensioners, organisations, states and territories that receive payments from the federal government.

Shadow treasurer Chris Bowen said the government appeared to be "pathologically incapable" of understanding people's opposition to the budget.

Mr Abbott insisted pensions were safe under his government.

The budget debate came as Labor leads the coalition by an average 55.6 to 44.4 per cent in two-party terms over three polls taken in the past week.

The government aims to put pressure on Labor next week with the reintroduction of the carbon tax repeal bills, which Mr Hockey told parliament would save state governments almost $700 million a year.